A randomised, double-blind, placebo-controlled study to evaluate the efficacy and safety of two doses (500 mg once daily and 500 mg twice daily) of GSK1605786A in maintaining remission over 52 weeks in adult subjects with Crohn's disease. Efficacy will be assessed by the Crohn's Disease Activity Index (CDAI) score. Eligible subjects will have achieved response (CDAI decrease of at least 100 points) and/or remission (CDAI less than 150) in a prior GSK sponsored induction study. The primary endpoint will be proportion of subjects in remission at both Weeks 28 and 52. Safety will be assessed by recording of adverse events, clinical laboratory parameters including liver function tests, vital signs and electrocardiogram. Population pharmacokinetics will evaluate the two doses of GSK1605786A. Health outcomes assessments will include changes in Inflammatory Bowel Disease Questionnaire (IBDQ), SF-36v2, EQ-5D, Work Productivity and Activity Impairment - Crohn's Disease (WPAI-CD) and disability.